Collaborative Research: Unsteady Ground Effect: How Solid Boundaries Affect Bio-Inspired Propulsion

许多动物在水面或海底附近飞行或游泳。 这些边界产生不稳定的、三维的和不对称的流动，可以增加动物的飞行/游泳速度和效率。尽管这些好处的广泛影响，有没有可靠的模型，近边界的生物运动。精确的模型可以重塑生物学家对鸟类在开放水域迁徙的飞行策略或对底栖鱼类形状的进化压力的思考方式。更好地了解近边界的生活方式可以帮助生态学家更好地预测近地面生态系统对过度捕捞，栖息地丧失或气候变化的脆弱性。更好的模型也将重塑工程师设计接近边界的生物启发车辆的方式。改进这些模型的关键是更好地理解控制近边界游泳和飞行的复杂流动。这项拟议的工作旨在阐明这些复杂的流动，并利用多媒体和针对中学女生的外展计划将其带入公众视野。 本计画的目标是了解近边界游泳的非定常流动机制。该项目将通过水槽实验和无粘流模拟相结合，支持对非定常地面效应的首次系统研究。因此，经典的稳定地面效应理论将被推广到现代跨学科的流动现象，目前在游泳和飞行的动物。这些流动现象将通过测试斯特劳哈尔数，减少频率，纵横比，波动和不对称运动学对近地面游泳的影响进行探讨。该研究将集中在四个具体目标：（一）开发缩放法律的力量和能量的近地面游泳，（二）映射近地面三维流的相互作用，（三）确定波动运动学在近地面游泳的作用，以及（四）了解如何不对称运动学改变近地面流。通过包括实验和无粘性模拟，研究将确定哪些效应是与雷诺数相关的，哪些效应纯粹是由无粘性涡动力学驱动的。 这项研究将为鱼类近地面生活方式提供关键见解，并将有助于设计新颖的生物启发水下航行器。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Many animals fly or swim near the surface of water or the ocean floor. These boundaries create unsteady, three-dimensional, and asymmetrical flows that can increase the animal's flying/swimming speed and efficiency. Despite the wide implications of these benefits, there are no reliable models for near-boundary bio-locomotion. Accurate models could reshape the way biologists think about the flight strategies of birds migrating over open water or the evolutionary pressures on the shapes of bottom-dwelling fish. A better understanding of near-boundary lifestyles could help ecologists better predict the fragility of near-ground ecosystems to over-fishing, loss of habitat, or changing climate. Better models would also reshape the way engineers design bio-inspired vehicles that operate near boundaries. The key to improving these models is a better understanding of the complex flows governing near-boundary swimming and flying. The proposed work aims to shed light on these complex flows and bring them into public view using multimedia and an outreach program for middle school girls. The goal of this project is to understand the unsteady flow mechanisms governing near-boundary swimming. The project will support the first systematic study of unsteady ground effect through a combination of water channel experiments and inviscid flow simulations. As a result, classic steady ground effect theory will be generalized to the modern interdisciplinary flow phenomena present in swimming and flying animals. These flow phenomena will be explored by testing the effects of Strouhal number, reduced frequency, aspect ratio, undulation, and asymmetric kinematics on near-ground swimming. The research will focus on four specific aims: (i) developing scaling laws for the forces and energetics of near-ground swimming, (ii) mapping near-ground three-dimensional flow interactions, (iii) determining the role of undulatory kinematics in near-ground swimming, and (iv) understanding how asymmetrical kinematics alter near-ground flows. By including both experiments and inviscid simulations, the research will identify which effects are Reynolds-number dependent and which are driven purely by inviscid vortex dynamics. This research will provide key insights into the near-ground lifestyles of fish and will aid in the design of novel bio-inspired underwater vehicles.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.